Management and Effects of Coalbed Methane Produced Water in the United States (2010)

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The extraction of methane (natural gas) trapped deep in some coal beds is a common practice, especially in Western States, but carries with it the issue of what to do with the water that must be pumped out to release the methane. This "produced" water must be managed through some combination of disposal, use, or storage, and often requires treatment to remove salts and other compounds. Currently, the majority of the water is disposed of at least cost, rather than being put to beneficial use, for example, for irrigation and as drinking water for livestock. This study investigates the critical environmental, economic, and regulatory issues associated with coal bed methane produced water, and finds that current management decisions often fail to consider both potential environmental effects and opportunities for beneficial use.

Key Messages

At present, the management of coal bed methane produced water is driven by consideration of the costs and regulations associated with treating and disposing of produced water, rather than by consideration of environmental effects or of potential beneficial uses of the water.

Continued research to resolve gaps in information on the chemistry of coal bed methane produced water, its effects on the environment, and the regulatory framework to best govern it, would permit the development of more effective and sound coal bed methane produced water management practices.

In addition to natural differences in water quality and quantity, some states' laws consider produced water a form of waste, while others consider it a beneficial byproduct of methane extraction, leading to widely different approaches among states in produced water management.

Produced water is thought to accumulate over millions of years, making it essentially a nonrenewable resource. Managing produced water therefore carries with it the responsibility to take all environmental considerations into account, rather than simply choosing the management option that comes at the least cost. Furthermore, the consequences of removing these stocks of water on local groundwater systems have not yet been thoroughly investigated.

Produced water varies greatly in both quality and quantity depending on the geology of the coal basin from which it is extracted, and sometimes requires treatment before disposal or use.

Produced water, after any required treatment, could be put to beneficial uses, for example for irrigation or drinking water for livestock. These potential beneficial uses have gained attention particularly in the western states where water is a much needed commodity.

Studies that used geochemical techniques to "date" coal bed water obtained from the San Juan Basin indicated that the water is thousands to tens of millions years old. This "fossil" water is non-renewable because it has not been replenished in human lifetimes. Scientists don't yet know if all coal beds store water of a similarly old ages—more data are needed to determine the age of produced water from other coal bed basins.

The extraction of water from coal beds and its eventual disposal or use can have either positive or negative impacts on soil, ecosystems, and the quality and quantity of surface water and groundwater. At present, no widespread negative effects have been documented. However, because coal bed methane production is a relatively young industry, these environmental impacts are not yet completely documented or understood.